Hi Guys ! I'm new here, so this is my firs post. I'm from Indonesia, and so manny betta keepers here. Mostly a kid, but they don't know how to keep betta fish the right way. 90% Betta in Indonesia are live in a jar, it's a sad fact. But here's my faithful friend. Name's glassy, because the first time i buy it the tail was in transparent/glass color. But maybe i give him too strong food so now the glass color is just a bit I put him in a bowl. I dont know how much the water capasity, i put a small rock and small fake grass to hiding spot. Any advice? how 'bout your comment? is taking care betta in a bowl not right?

Hello and welcome! Your fish is beautiful!
You technically can keep a betta in a bowl if it's large enough (some argue about whether 1 US gallon or 2.5 US gallons is the minimum) and has a heater. They do like room to swim and you will see his personality come out more when he gets more room, so I like keeping them in at least a 5 gallon tank with a filter so then another benefit is you can cycle it and not have to change the water as frequently. His water should be between 76 and 82 degrees F (24 to 27 degrees Celcius).
Has his tail grown since you got him? He might have had finrot previously, and his tail was just growing back when you got him. Usually new fin growth is clear.

since you're in indonesia, you should try going to a creek or pond and collecting some native water plants for him. just make sure to only pick bright green specimens with no rotting leaves, and keep them in a separate tank, or bucket or jar, as long as it's water filled and clean (no chemicals or residue or anything like that) for a few weeks to make sure it's not got any tag-a-longs that could hurt him, then plant them in his bowl. they give him lots of places to explore, leaves to rest on, and most importantly they help to neutralise the ammonia he produces, keeping your water cleaner in between changes. seeing as you're in a tropical country, i doubt you'd need a heater unless you artificially cool your home significantly.